1. Field of the Invention
The present invention relates generally to a chair of the type suitable for use in an office environment and, more particularly, to a reclining office chair having several structural and operating features which offer a number of ergonomic and other advantages over the prior art.
2. Description of the Related Art
Over many years attempts have been made to design chairs for use in office environments which are comfortable to use and thereby avoid user fatigue over prolonged use. In one simple form a chair may be provided with a swivel base for ease of turning and include a control mechanism which permits the chair to rock. A disadvantage of these relatively simple chairs is that conjoint rocking motion of the chair seat and back naturally lifts the user""s feet off the floor, which can create stability problems and place upward force on the front of the user""s thighs which can reduce fluid circulation in the user""s legs.
To improve on the foregoing chair construction, chair controls are known which provide for synchronous movement of the chair seat and back. Where office chairs are concerned, a xe2x80x9csynchronous controlxe2x80x9d means the arrangement of a combined or dependent back adjustment and seat adjustment, that is to say the adjustment of the back inclination fundamentally also results in an adjustment of the sitting surface. An example of a synchronous chair control is disclosed in U.S. Pat. No. 5,318,345, issued to Olson and assigned to the common assignee herein. With the aforementioned Olson control, the chair back is designed to tilt at one predetermined rate of recline while the seat tilts synchronously at a much lesser rate. The result is that the user""s feet are not lifted from the floor when the back is reclined. Also, fluid circulation in the user""s legs is not interrupted by substantial upward movement of the forward end of the seat. Another advantage of this control is that undesirable xe2x80x9cshirt pullxe2x80x9d is minimized by the strategic location of the tilt axis. Other examples of synchronous chair controls are disclosed in U.S. Pat. Nos. 5,366,274 and 5,860,701, to name a few.
In U.S. Pat. No. 6,125,521, it is disclosed to be desirable to provide a chair having a seat and backrest which pivot generally about the axis of the hip joints of the user. A disadvantage of that chair is that as the chair back reclines, the rear of the seat also tilts downwardly, having the effect of changing the user""s gaze angle. Further, in that chair, the arms also tilt with the chair back, thus displacing the user""s arms away from any work surface. In U.S. Pat. No. 5,979,984, the seat is arranged to both slide forwardly and the rear portion of the seat moves downwardly as the back reclines.
Another feature embodied in recently designed office chairs that offers considerable ergonomic advantages is a tilt limiter feature for the chair back. With such a mechanism built into the chair control, the user may selectively set the degree of back recline at a predetermined angle thereby adding to comfort as the chair is used. An example of such a tilt limiter mechanism is disclosed in U.S. Pat. No. 6,102,477 issued to Kurtz and assigned to the common assignee herein. This particular mechanism offers the advantage of providing for infinitely variable angles of tilt within a predetermined overall range. The mechanism is also highly cost-effective to construct.
Yet another feature of current ergonomically designed chairs is the provision of height and pivot adjustable arm pads. Such a feature is particularly advantageous in providing the user with additional support to the arms, forearms, wrists and shoulders in order to minimize repetitive stress injuries when the user is keyboarding, for example, while seated in the chair. An example of such an adjustable arm pad using a gas cylinder is disclosed in U.S. Pat. No. 5,908,221 issued to Neil.
Yet another feature of current ergonomically designed office chairs includes an adjustable lumbar support mechanism for providing preselected chair back tension in the region of the user""s lower back. An adjustable lumbar support allows the chair user to select a comfortable level of pressure on the lower back depending upon the specific office task being performed. Such a mechanism is disclosed, for example, in U.S. Pat. No. 5,797,652.
Still another feature of certain ergonomically designed office chairs, particularly of recent vintage, is the incorporation of fabric mesh into the construction of the chair seat, and/or back. These materials ostensibly offer the advantage of enhanced air circulation for and consequent heat transfer from the chair user""s body, which can improve the comfort of the chair. An example of the use of such fabric mesh in an office chair is disclosed in aforementioned U.S. Pat. No. 6,125,521 issued to Stumpf et al.
Yet another feature of certain ergonomically designed chairs is the provision of a seat cushion having the capability of effecting heat transfer from the chair user""s buttocks area while at the same time offering comfort to the user while seated, together with adequate support. Known seat cushions having such capability may involve a passive or active air flow circulation feature of the type disclosed, for example, in U.S. Pat. No. 6,179,706.
The present invention provides a totally redesigned ergonomic chair that incorporates simple but improved functional and esthetic aspects in all areas of a modular chair construction and in its use, including synchronous tilt of back and seat; tilt limit control; separate seat adjustment; arm adjustment; adjustable lumbar support; cushion airflow; mesh attachment and modular base frame assembly.
The various subfeatures of these various components are the subject of the following individual applications, the parent applications of each of which were filed on the same date as the parent application of the present case, the continuation-in-part applications being filed on even date herewith, all commonly assigned, the disclosures of all of which are incorporated herein in fall by reference:
Multi-position Tilt Limiting Mechanism U.S. Ser. No. 09/882,500, filed Jun. 15, 2001
Locking Device for Chair Seat Horizontal Adjustment Mechanism U.S. Ser. No. 09/881,896, filed Jun. 15, 2001 and Adjustable Chair Seat Locking Mechanism Continuation-in-part application, Application No. 10/077,313, filed on even date herewith
Height and Pivot-Adjustable Chair Arm U.S. Ser. No. 09/881,818, filed Jun. 15, 2001 and Vertically and Horizontally Adjustable Chair Armrestxe2x80x94Continuation-in-part application, Application No. 10/077,073, filed on even date herewith
Lumbar Support for a Chair U.S. Ser. No. 09/881,795, filed Jun. 15, 2001
Body Support Member U.S. Ser. No. 09/882,503, filed Jun. 15, 2001 Continuation-in-part application, Application No. 10/172,699, filed Jun. 14, 2002
Chair Back Construction U.S. Ser. No. 09/882,140, filed Jun. 15, 2001 and Chair Back Constructionxe2x80x94Continuation-in-part application, Application No. 10/077,540, filed on even date herewith
Chair of Modular Construction U.S. Ser. No. 09/881,897, filed Jun. 15, 2001
In each of these cases, features combine to provide an overall chair that is a significant improvement over the prior art.
Thus, for example, the present invention provides a reclining chair having a four bar linkage system that causes the rear of the seat to elevate as the back is reclined lending an unusual and comfortable balance during reclining. A very simple and economically constructed tilt limit control conveniently and effectively limits the degree of chair back tilt to one of several reclined positions by manual movement of a lever. Horizontal positioning of the chair seat cushion may be accomplished using a simple but positive locking device that allows the chair user to select a preferred horizontal seat cushion position. Height and pivot adjustable chair arms are simply and positively actuated with the push of a button or simple rotation, lending convenient adjustment to suit a specific work task. A lumbar support is easily height adjustable, by providing tension to the back frame and requires no screws or adjustment knobs in its adjustment mechanism, and also does so by avoiding direct contact of the lumbar support with the back of the user. A modular cushion seat includes a comfortable thermal air flow layer and gel layer which is vented uniquely for air circulation and stress and pressure management. The back of the chair is of fabric mesh construction and includes a novel attachment system for superior comfort. The base and back of the chair are of modular construction that provides for ease of assembly and lends rigidity to the chair construction, and in which an open skeletal frame structure displays both the simplicity of the chair structure while adding to its esthetic appeal.
A primary object of the present invention is a tiltable chair wherein users of substantially all weights and sizes may be continuously balanced in the chair at any selected reclination position, therefore enhancing both xe2x80x9cfitxe2x80x9d and xe2x80x9ccomfort.xe2x80x9d The present invention improves over the prior art by providing an ergonomic chair having a four-bar linkage arrangement wherein a lower frame member is provided with a rigid front support and a rigid rear support with a seat member pivotably connected to the front support. A back rest has a first pivot point connected at an upper end of the rear support of the lower frame member. A link member pivotably connects at a first end to a rear support of the seat member and at a second end to a second, lower pivot point on the back rest. This novel arrangement permits tilting movement of the backrest rearwardly relative to the lower frame member while concurrently causing elevation of a rear portion of the seat member, permitting the feet to remain on the floor and alleviating pressure on the user""s thighs. This is accomplished by a linkage mechanism creating an instantaneous center of rotation of the chair seat and back that is approximately at the user""s hip, so that the movement of the seat and back reduces undesirable xe2x80x9cshirt pull.xe2x80x9d This arrangement also is more responsive to the user and provides correct back support throughout tilt.